These edges are made by the edges on the hollow of each ice skate (and the direction of the skater). One turns in ice skates by leaning on one of these edges. For example, if I am going forward and I am on my left foot, I can turn left by leaning on my left forward inside edge. I can turn right by leaning on my left forward outside edge. You may be wondering why have eight instead of four. The reason that eight are specified instead of four is to allow you to describe transitions from one to the other. For example, I can transition from the left forward inside to the right backwards inside in one move.